The present invention relates to protective devices for use in deflecting or reducing short duration, large current, artificially or naturally created electromagnetic impulses traveling along a radio frequency (RF) cable, while allowing desired RF signals to pass through.
Short duration, large current, artificially created electromagnetic impulses, such as produced by motors, switches or certain types of electrical circuits or naturally created electromagnetic impulses such as produced by lighting and transmitted through RF cables may damage or even destroy the equipment which may be connected to these cables.
In the past, such equipment has been protected by devices which eliminate or deflect such impulses.
One such device comprises an elongated cylindrical housing having connectors at each end which serves as an outer conductor, an elongated pin axially disposed within the housing which serves as an inner conductor, insulators for electrically separating the outer conductor from the inner conductor and a gas discharge tube (GDT) electrically coupled between the outer conductor and the inner conductor. The GDT is mounted in a hole formed in the sidewall of the housing and is pushed down in the hole into electrical contact with the inner conductor by a spring and an end cap. This arrangement for mounting the GDT inside the protective device is costly and not very satisfactory.
In U.S. Pat. No. 4,359,764 to Roger R. Block there is disclosed a connector for the suppression of electromagnetic impulses traveling along a radio frequency cable. Paired first and second electrical connectors are provided for being operatively interposed along the signal cable. A spacer or mounting device is provided for electrically coupling the primary conductors and secondary conductors of one connector to their counter parts in the other paired connector. A gas discharge tube having a known breakdown voltage and a known capacitance is electrically and mechanically coupled between the first and second conductors of the mounting device. The inductance of the elements comprising the mounting device are determined such that this inductance interacts with the capacitance of the gas discharge tube and other stray capacitance of the combination thereof in order to produce a characteristic impedance which is generally equal to the characteristic impedance of the radio frequency signal cable, whereby the suppressor will dissipate electrical surges while representing low standing wave ratio to radio frequency energy being transmitted along the radio frequency signal cable.
In U.S. Pat. No. 4,409,637 to Roger R. Block there is disclosed a connector for the suppression of electromagnetic impulses traveling along a radio frequency transmission line. Paired first and second electrical connectors are provided for being operatively interposed along the transmission line. First and second conductors are provided for electrically coupling the primary conductors and secondary conductor of one connector to their counterparts in the other paired connector. A discharge device or tube having a known breakdown voltage and a known capacitance is coupled between the first and second conductors. A capacitor is coupled in series with the first conductor for blocking the flow of dc energy there through. The inductance of the first and second conductors are determined such that this inductance interacts with the capacitance of the discharge device, and the capacitor and other stray capacitance of the combination thereof in order to product a desired characteristic impedance, which is generally preferred to be equal to the characteristic impedance of the radio frequency transmission line, whereby the suppressor will dissipate electrical surges while representing a low standing wave ratio to radio frequency energy being transmitted along the line. In an alternate embodiment, a ground plane is provided for reducing the effective size of a balanced line embodiment thereof.
In U.S. Pat. No. 4,554,608 to Roger R. Block there is disclosed a connector for the suppression of electromagnetic impulses traveling along a radio frequency transmission line. Paired first and second electrical connectors are provided for being operatively interposed along the transmission line. First and second conductors are provided for electrically coupling of the primary conductors and secondary conductors of one connector to their counterparts in the other paired connector. A discharge device or tube having a known breakdown voltage and a known capacitance is coupled between the first and second conductors. First and second capacitors are coupled in series respectively with the first and second conductors for blocking the flow of dc energy there through. The inductance of the first and second conductors are determined such that this inductance interacts with the capacitance of the discharge device, and the two capacitors and other stray capacitance of the combination thereof in order to produce a desired characteristic impedance, which is generally preferred to be equal to the characteristic impedance of the radio frequency transmission line, whereby the suppressor will dissipate electrical surges while representing a low standing wave ratio to radio frequency energy being transmitted along the line. The two capacitors prevent the flow of dc energy along the transmission line in order to protect the electronic equipment connected thereto.
In an alternate embodiment, a second capacitor and discharge device are utilized in order to provide additional differentiation and clamping of the impulse signal. An embodiment is also disclosed for inserting and removing a control signal along the center conductor.
In U.S. Pat. No. 5,764,114 to Gregor Kxc3xchne there is disclosed an electromagnetic pulse filter which can be used simultaneously for a plurality of frequency bands. The filter includes a housing mounted in the outer conductor and a xcex/4 short-circuiting conductor, which is connected in an electrically conductive fashion to the inner conductor of a coaxial line and is connected in an electrically conductive fashion to the end face of a housing. Arranged between the housing and the short-circuiting conductor is at least one sleeve which is connected to the latter in a conductive fashion. The length of the short circuiting line corresponds to the xcex/4 length of the lowest frequency band transmitted. Considered together, the sleeves produce a number of cavity resonators which are connected in series and are tuned with their length to various midband frequencies. It is directly possible by means of such cavity resonators connected in series to transmit a plurality of frequency bands, and thus to protect terminals against damaging current surges.
In U.S. Pat. No. 6,101,080 to Gregor Kxc3xchne there is disclosed a de-coupled EMP-charge eliminator device in a co-axial cable, with the charge eliminator component in electric contact with conductor leading to the internal conductor of the co-axial lead, and with a housing attached to an external conductor, whereby a concentrated capacitor is inserted, in parallel, between the housing and the conductor, and the charge eliminator is placed between the capacitor and the housing and that this becomes, via the capacitance of the capacitor, a RF-short circuit breaker so that conductor acts as a lamda/4 short-circuit conductor.
It is an object of this invention to provide a new and improved protective device for deflecting or reducing short duration, large current electromagnetic impulses traveling along an RF cable while allowing desired RF signals to pass through.
It is another object of this invention to provide a protective device as set forth above and having an outer conductor, an inner conductor and a protective element between the outer conductor and the inner conductor and wherein the protective element is mounted within the protective device in a new and novel manner.
In furtherance of the objects broadly set forth above there is provided a protective device for suppressing short duration, large current, electromagnetic impulses which may occur along a RF cable, said protective device including among other things in accordance with one aspect of the invention, an outer conductor and an inner conductor, said outer conductor comprising a main body section, a first connector and a second connector, said main body section having a first end and a second end, said first connector extending out from the first end of the main body section, said main body section comprising a housing having an inner sidewall, said second connector being mechanically mounted on and extending out from the second end of the main body section, an inner conductor axially disposed within the outer conductor, insulators for mechanically supporting and electrically insulating the inner conductor from the outer conductor, a protective element disposed inside the main body section between the inner sidewall in the main body section and the inner conductor, and a spring of electrically conductive material disposed inside the main body section between the protective element and the main body section in contact with said sidewall and said protective element, said spring and said protective element providing a current path from the inner conductor through the protective element to the inner sidewall.
According to another aspect of the invention the impedance through the length of the device is controlled to optimize RF performance.
Additional objects, as well as features and advantages, of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.